This invention relates to the problem of transmitting varying types of data between stations connected in a digital loop format.
The ability to transfer data from one point to another is fast becoming the backbone of our industrialized society. As data transmission becomes more and more popular the level of sophistication required also rises. Thus, we find a situation developing wherein, especially in the business environment, any terminal connected to the switching network must be capable of handling any type of data presented to it in an efficient and universal manner.
While such remains the goal, the problem is compounded in that the data from differing types of equipments arrive at the data terminal in differing forms and at differing rates. For example, data which is representative of speech is usually continuous in nature. For this reason it follows that when voice data is being transmitted it is necessary to establish a continuous or "circuit switched" connected through the network. On the other hand, data from a computer terminal or from a temperature sensor, arrives in spurts and is thus "bursty" in nature. Such bursty data must be immediately forwarded when it appears at the terminal, but due to its bursty or noncontinuous nature many such independent bursty data inputs may be interleaved in a given period of time.
One solution to the problem of handling both continuous and bursty data types is shown in the commonly assigned co-pending patent application filed concurrently herewith, Ser. No. 062,422.
Using the teachings of said co-pending application, which is hereby incorporated by reference as though completely reproduced herein, both bursty and continuous data are interleaved on a single channel from a group of stations located at a common point. The interleaving occurs under control of a programmable station controller. The problem then remains to distribute the data to the proper receiving stations via the receiving station's programmable station controller. To state the combined from each location onto a single data loop channel that data must be separated and delivered to the proper destination. Thus, a delivery system must be designed to separate the bursty data from each frame and to deliver that data packet to the proper address. Since the destination address will change with each word frame, dedication of time slots in the delivery system becomes difficult and a housekeeping nightmare. At the same time it is important to reserve space in each delivery frame for the transmission of the continuous data, which for any one call must be delivered to the same location on each frame.
Digital loop systems designed in a backplane mode solve many of the problems of data delivery to various locations within a definable grouping of stations and such systems are now well known in the art. For example it is known to handle bursty data in a packetized manner. One example of such a packet switched digital loop is T. J. Pedersen U.S. Pat. No. 4,154,983. A loop scheme for continuous data transfer is shown in D. E. Blahut et al. U.S. Pat. No. 3,781,478. While each of these schemes adequately handle the type of information transfer for which they are designed, each has problems handling data of the other type. These problems arise primarily because of the diametrically opposed traffic characteristics of each data type.
The above-mentioned Pedersen disclosure recognizes the problem of handling different type data within each frame by separating the two types of data. However, in Pedersen the central controller performs all of the control functions and thus each word must be assigned first to the time slot associated with the transmitting station and then, under control of the controller, be moved to the time slot assigned to the receiver station. This places a large load on the controller and effectively reduces the amount of traffic that can be handled. In addition, since the data interchange between the stations is controlled by the central controller, only one such interchange may occur in any given frame.